Methylhydrogenpolysiloxanes are widely used as various types of surface treatment agents used for cosmetics. A powder that has been treated using methylhydrogenpolysiloxane is highly water repellant and thus is characterized as improving the ability to prevent the smearing of makeup. However, in addition to reacting with the particle surface at the time of surface treatment, methylhydrogenpolysiloxane also triggers crosslinking reactions between molecules. Thus the percentage of reaction with the surface is low, and this results in remnant unreacted Si—H bonds in the surface-treated powder. Thus, depending on conditions, there is the possibility of generating hydrogen gas, and such hydrogen gas is dangerous in the presence of fire or the like. Further, various types of problems have occurred due to use of methylhydrogenpolysiloxane, such as expansion of cosmetic containers, clouding of compact mirrors, and the like. Various methods have been proposed so that remnant Si—H bonds are not generated. Such methods include a method of surface treatment using a single end alkoxy-modified silicone as described in Japanese Unexamined Patent Application Publication No. H07-196946, and a method of surface treatment using an acrylic-modified silicone having an alkoxysilyl group as described in WO 2002/100356. However, the alkoxy group content is low when the single end alkoxy-modified silicone is used, and thus the method using the single end alkoxy-modified silicone has had a problem of low reactivity with the powder. On the other hand, the method of surface treatment using the acrylic-modified silicone having an alkoxysilyl group uses an acrylic-modified silicone produced by grafting a linear silicone to an acrylic main chain, and thus there has been a problem of insufficient sebum resistance and the like. Moreover, the powder that has been surface-treated using the acrylic-modified silicone having an alkoxysilyl group has had problems in that compatibility with other cosmetic raw materials is low, and compounding stability of the cosmetic has been poor.
Cosmetic raw materials have been proposed that have, as a main agent, a vinyl-based polymer that has a carbosiloxane dendrimer structure, or a vinyl-based polymer that has both a carbosiloxane dendrimer structure and a fluorine-containing organic group (see Japanese Unexamined Patent Application Publication No. 2000-063225 and Japanese Unexamined Patent Application Publication No. 2003-226611). However, in Japanese Unexamined Patent Application Publication No. 2000-063225 and Japanese Unexamined Patent Application Publication No. 2003-226611, there is no mention of use in surface treatment of various types of powders. Moreover, Japanese Unexamined Patent Application Publication No. H09-136812 proposes a copolymer that is obtained by copolymerization of a radical-polymerizable monomer, an organopolysiloxane compound that has a radial-polymerizable group at one molecular chain terminal, and N-vinylpyrrolidone. However, this copolymer has no hydrophilic group, the copolymer particularly does not have an alcoholic hydroxyl group, and there is no description of use in the surface treatment of various types of powders.
Further, although the blending of the copolymer in a cosmetic as a film-forming agent is disclosed, the copolymer has had a problem in that dispersibility and compounding stability are insufficient particularly when the copolymer is used with a powder used in cosmetics. In order to solve such problems, the authors of the present application propose a cosmetic raw material and powder treatment using a specific polymer having a carbosiloxane dendrimer structure in Japanese Unexamined Patent Application Publication No. 2011-149017 and Japanese Unexamined Patent Application Publication No. 2011-148784. In comparison to previously existing powder treatment agents, these polymers have greatly superior dispersibility, compounding stability in the cosmetic, or the like. However, these polymers still have margin for improvement in dispersion performance particularly when a fluorine-treated powder or the like is blended in the cosmetic. Also after the cosmetic containing the powder has been coated onto the skin, sometimes dispersion failure occurs on the skin, i.e. agglomeration of the powder due to volatilization of a liquid oil agent or the like. Further, there has been neither mention nor suggestion concerning the relative proportion of the specified carbosiloxane dendrimer structure composing the copolymer. Also there has been neither mention nor suggestion concerning combined use with a monomer that has a hydrophilic functional group.